Method for calculating dielectric versus air void content relationship for asphalt concrete using a single calibration measurement

Abstract

A method for generating a calibration curve of asphalt concrete of a known mix. Initially, a single sample of the known asphalt concrete mix is obtained. The single sample has a known percent voids. A dielectric measurement of the single sample is obtained. Using only the dielectric measurement of the single sample, the sample's known percent voids, and a dielectric of air, a theoretical ideal dielectric for the asphalt concrete mix at 0% voids is computed. A dielectric vs. percent voids calibration curve is generated based on the computed ideal dielectric.

The invention claimed is: 
     
       1. A method for generating and using a calibration curve of asphalt concrete of a known mix, the method comprising:
 obtaining a single sample of the asphalt concrete mix, the single sample being formed as a puck or core extracted from paved asphalt and having a known percent voids; 
 obtaining a dielectric measurement of the single sample; 
 using only the dielectric measurement of the single sample, computing an ideal dielectric for the asphalt concrete mix at 0% voids; 
 generating a dielectric vs. percent voids calibration curve based only on the dielectric measurement of the single sample and on the computed ideal dielectric, 
 obtaining a second sample of the asphalt mix, the second sample having an unknown void percentage; 
 measuring a second dielectric of the second sample; 
 comparing the second dielectric to the calibration curve; and 
 when the second dielectric is off the calibration curve, decomposing and analyzing the second sample to identify a change in the asphalt mix or in an environment surrounding the asphalt mix. 
 
     
     
       2. The method of  claim 1 , wherein the computing of the ideal dielectric is based on the equation 
       
         
           
             
               ϵ 
               = 
               
                 
                   ( 
                   
                     
                       ϵ 
                       s 
                     
                     + 
                     
                       f 
                       
                         
                           1 
                           
                             
                               ϵ 
                               i 
                             
                             - 
                             
                               ϵ 
                               s 
                             
                           
                         
                         + 
                         
                           
                             1 
                             - 
                             f 
                           
                           
                             3 
                             ⁢ 
                             
                               ϵ 
                               s 
                             
                           
                         
                       
                     
                     + 
                     
                       ϵ 
                       i 
                     
                     + 
                     
                       
                         1 
                         - 
                         f 
                       
                       
                         
                           1 
                           
                             
                               ϵ 
                               s 
                             
                             - 
                             
                               ϵ 
                               i 
                             
                           
                         
                         + 
                         
                           f 
                           
                             3 
                             ⁢ 
                             
                               ϵ 
                               i 
                             
                           
                         
                       
                     
                   
                   ) 
                 
                 / 
                 2 
               
             
           
         
         where: 
         ∈ is the dielectric measurement of the single sample; 
         ∈ e  is the ideal dielectric of the asphalt mix with 0% voids; 
         ∈ i  is the dielectric of air; and 
         f is a volume fraction of air in the single sample. 
       
     
     
       3. The method of  claim 1 , further comprising:
 when the second dielectric is on the calibration curve, extracting from the calibration curve a second air void percentage of the second sample. 
 
     
     
       4. The method of  claim 1 , further comprising, in response to identifying the change in the asphalt mix or in the environment, modifying the asphalt mix to match the calibration curve. 
     
     
       5. The method of  claim 1 , further comprising, in response to identifying the change in the asphalt mix or in the environment, computing an updated calibration curve for the changed asphalt mix or at the changed conditions. 
     
     
       6. The method of  claim 3 , further comprising:
 comparing the extracted second air void percentage to an expected air void percentage; and 
 when the extracted second air void percentage is distinct from the expected air void percentage, decomposing an analyzing the second sample to identify a change in the asphalt mix or in an environment surrounding the asphalt mix. 
 
     
     
       7. The method of  claim 1 , wherein the ideal dielectric of a mix is generated from the average or median of ideal dielectrics calculated individually from two or more asphalt samples.